Since I dumped cable and went to Dish Network, I really can't say anything bad about either in all honesty. At least in my area, both options provide fairly stable service, and with that said it's more or less a question of which option is going to give me a better rate on HD programming. As of about a year ago, when I dumped cable for Dish, the cable around here only had about 8 HD channels, and a lot of the programming was in 720p. Now, Dish is the only provider to my knowledge that is putting out true 1080i, the other providers are using 720p still, at least that's my understanding of the other sat options, not sure about cable.
The channel selection is pretty good, though I haven't seen DirectTV's HD lineup or pricing, I'm assuming it's probably comparable. As of the day I'm writing this review, we just had a major blizzard about an hour ago, and the dish wasn't cutting out at all, so I can say that at least our equipment they've provided is quality stuff.
The pricing though, well, it is a bit ridiculous. You can't really get a basic package with the HD channels. You usually have to fork out quite a bit if you want the HD channels. So, definitely shop around if you're chasing a good HD package.